Molecular Masses of Some Common Elements
Element | Symbol | Atomic mass | Molecular formula | Molecular mass |
---|
1.Hydrogen 2.Nitrogen 3.Oxygen 4.Chlorine | H N O Cl | 1 u 14 u 16 u 35.5 u |
| 2x1 = 2 u 2 x 14 = 28 u 2 x 16 = 32 u 2 x 35.5 = 71 u |
We will now solve a problem based on the calculation of molecular mass of a compound.
Sample Problem. Calculate the molecular mass of sulphuric acid (
).
(Given : Atomic masses : H = 1 u ; S = 32 u ; O = 16 u).
Solution. The molecular formula of sulphuric acid is
.This formula shows that one molecule of sulphuric acid (
) contains 2 atoms of hydrogen,1 atom of sulphur and 4 atoms of oxygen. So, the molecular mass of H2S04 will be equal to the sum of the masses of 2 hydrogen atoms, 1 sulphur atom and 4 oxygen atoms. Knowing that the atomic mass of hydrogen is 1 u, of sulphur is 32 u and that of oxygen is 16 u, the molecular mass of sulphuric acid can be calculated as follows:
Molecular mass of
= Mass of 2H
atoms + Mass of S
atom + Mass of 4 'O'
atoms
= 2x1+32 + 4x16
= 2 + 32 + 64
= 98 u
Thus, the molecular mass of sulphuric acid is 98 u.
Before we conclude the discussion on formulae, it will be good to note the significance of the chemical formula of a substance which is given below.
Notes
Atoms and Molecules - Notes
1. Monovalent Cations (Cations Having a Valency of 1+)
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3. Divalent Cations (Cations Having a Valency of 2+)
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4. Trivalent Cations (Cations Having a Valency of 3+)
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6. an example, let us give the significance of symbol C
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7. Formulae of Some Molecular Compounds
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10. Simple Ions and Compound Ions (Polyatomic Ions)
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11. Explanation of the Law of Conservation of Mass
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12. Molecular Formulae of Some Common Elements
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13. 2. A Negatively Charged Ion is Known as Anion
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14. As an example, let us give the significance of the formula H
2O
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20. Gram Atomic Mass And Gram Molecular Mass
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28. 1. A Positively Charged Ion is Known as Cation
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34. Divalent Anions (Anions Having a Valency of 2-)
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36. Molecular Masses of Some Common Elements
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38. Significance of the Formula of a Substance
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39. Explanation of the Law of Constant Proportions
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42. Symbols Derived from Latin Names of the Elements
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45. Valencies of Some Common Metal Elements Valencies of Some Common Non-Metal Elements
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46. Atomic Masses of Some Common Elements
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48. Writing Of Formulae Of Molecular Compounds
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50. Writing Of Formulae Of Ionic Compounds
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